Stephen Compall wrote:
On Sun, 2007-05-20 at 19:39 -0700, Tomas Melchior wrote:
What platforms/implementations support this? The manual only says "some
Lisps". Also, is there anything analogous to lambda for defcallback?
To refer to the text:
*Portability note:* `defcallback' will not work correctly on some Lisps
if it's not a top-level form.
The point of this note is to say that CFFI doesn't guarantee that it
will work, much as doing anything not defined by ANSI Common Lisp isn't
guaranteed to work in portable Common Lisp code. In fact, "some" may
mean "none at all" now or at any future time. In other words, don't do
it.
I wonder if we even want to word this more strongly and outright declare
the results undefined or implementation-defined if at non top-level.
DEFCALLBACK is one place that we compromise and pass through to the
Lisp's underlying DEFCALLBACK macro, instead of using a functional
interface. Unfortunately, this can allow implementation details to
leak through, as it does in this case.
I would love to see all supported Lisps providing the underlying
machinery to make a CALLBACK-LAMBDA happen, but I think the number
is currently quite low. :( I did write a patch awhile back adding
this for (IIRC) SBCL and CLISP. It should be in the cffi-devel list
archives.
With a widely supported CALLBACK-LAMBDA, we could implement DEFCALLBACK
in terms of CALLBACK-LAMBDA, as we do with DEFCFUN and FOREIGN-FUNCALL.
I'd like to hope we can get there someday...
James
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